The carbon-fiber-reinforced polymer sheets (CFRP) and steel jackets are typically used for strengthening of the concrete columns. In the current study, a new approach is considered for the columns retrofitted applying those materials simultaneously. The effect of hybrid methods on the performance of columns under lateral loading is investigated numerically. For this purpose, the numerical models are verified using valid laboratory tests on the columns confined with FRP or steel jackets. Strengthening methods of concrete columns in the present study include the combination of a CFRP layer of different thicknesses and a steel cage, which is made as a complete steel jacket or the combination of L-shaped sections with steel bands. The results show that the concurrent use of steel jacketing and CFRP wrapping techniques increase the bearing capacity of the column, up to 4 times the bearing capacity of the unreinforced column. The alternative steel jackets composed of the connection strips lead to better performance in terms of the increasing strength, as well as the ease of execution. Ultimately, it should be noted that the presence of carbon fibers reduces the ductility of the studied columns.

In this paper, application of rectified square steel jackets for improving the hysteretic behavior of reinforced concrete column has been investigated. Deficient performance of square steel jacket due to out of plane bulging in cross section under moderate and severe earthquake excitations and having an advantage of taking less space after retrofitting, strengthenin of square steel jacket in potential plastic hinge regions can be useful means for achieving appropriate performance of this type of steel jacket. In the present study, all of the analyses have been undertaken using ANSYS (version 10.0). In order to verify the accuracy and validity of the finite element modeling, the numerical results, obtained from nonlinear finite element analyses, have been compared with the available experimental data. Having verified the finite element modeling, a deficient RC column designed according to pre-1971 codes was selected and eleven specimens with different states of retrofitting details were used for reinforcement ofsquare steel jacket in potential plastic hinge regions. Also, the effects of increase in thickness of plate stiffeners, geometric shape of stiffeners and stiffened length of column have been investigated. The results of analyses indicate that energy dissipation and shear strength at rectified steel jacketed specimens significantly are improved by increasing the thickness of steel plate stiffeners until achieving maximum flexural strength of cross section and also stiffened height of column. However, geometric shape of stiffeners does not have a drastic effect on the hysteretic behavior of retrofitted column.

In recent decades, concrete column retrofitting methods and their seismic behavior under cyclic loading, especially from ductility and energy absorption standpoints, have been extensively focused by researchers. Significant amount of this research has been allocated to confinement of concrete elements in order to advance the ductility and energy absorption capability of the concrete structures facing the forces induced by earthquake. In this study four methods of concrete column retrofitting methods, including FRP plates, steel jackets, and concrete jackets, have been assessed and thoroughly compared with each other in terms of seismic behavior advancement measurements.
To achieve this objective, different retrofitting methods were simulated in ABAQUS FEA software, based on prominent finite element analysis and numerical modeling. The modeling results were verified with equivalent experimental tests which further validates the accuracy of the modeling approach. In addition, the impact of the following variables were studied using sensitivity analysis on the replicated models: Core concrete strength, texture and number of layers of FRP plates, size and thickness of steel plates, and dimensions of concrete jacket, along with diameter and placing of stirrups and bars.
Strength, ductility, and energy absorption capacity of the simulated models were recorded in order to compare efficiency of each retrofitting method. Results have shown that retrofitting through FRP plates leads to increasing ductility. Retrofitting using concrete jackets, despite increasing the energy absorption capability and maximum shear strength, will not result in acceptable ductility. On the under hand steel jackets, along with improving a maximum shear strength and energy absorption ability of the element, shows promising improvement in ductility. Moreover, for the models with the same axial load and lateral load capacity, steel jacketing and concrete jacketing methods have proved to show better ductility, compared to FRP. Plus, steel jacketing resulted in the highest energy absorption capability among all the three methods under the aforementioned condition.

Performance of reinforced concrete frames is highly depended on detailing of the ductile connections based on the philosophy of strong column-weak beam. There are several methods for seismic upgrading of connections. In this paper, using steel jacketing for seismic upgrading of Concrete Beam-Column connections subjected to constant axial and cyclic loads has been investigated using finite element method. Some experimental results are used to verify the finite element approach. Analyses are then conducted on main models upgraded with steel jackets in beam, column or both using parameters like beam jacket thickness, column jacket thickness and axial load ratio. The results are compared and the suitable model is proposed. Based on different analysis for the considered samples, several results obtained. Analysis result shows the positive impact of the use of steel jacketing for upgrading of Concrete Beam-Column connections. From these results, it can be noted that, regardless of the size of the axial load, using a steel plate increased the tangential rigidity of connection. And this increasing of rigidity in most cases is more than of increasing of final capacity of the connection. But in the case of high axial loads, the increase that can be seen in the final capacity of the connection is further of rigidity increasing. Also, depending on the size of the axial load, steel plate can increase the capacity of connection up to 7 time, and the capacity and ductility of connections was returned to better state with the average axial load.

This research numerically investigates the structure behavior of steel jacket platform stand on 20 degrees inclined seabed and exposed to the earthquake. Considering the inclined seabed, the effect of the main variables on the structural behavior of the steel jacket platform subjected to the four famous earthquakes are discussed. The most effective variables of the structural response contain stresses and displacement. The stresses and displacement of the main four legs and as well as at the top of jacket structure will be as indicator for the structural response. ABAQUS 6.14 is used to model and analyze. The research finds that the change in the mass location will generate torsion effects which vary according to the leg's location and its length. In the sloping seabed it is necessary to use a stiffer tubular section to resist the torsional effect.

Nowadays, reinforced concrete structures are widely being constructed all over the world and some of them need to be strengthened for variety of reasons such as poor design, damages caused by earthquakes, etc. Nowadays, engineering attitude toward demolition and renovation of structures have been changed to retrofitting and upgrading. By retrofitting, the structural reliability increases and saves both time and cost. In some of special cases that the structure can not be demolished and rebuilt, retrofitting plays an important role. The columns of the structures are one of the main elements that are subjected to axial, shear forces, and bending moments, and their strength and ductility have an important impact on their seismic capacity. Different methods are used for strengthening of columns. These methods include concrete jacketing, steel jacketing and composite jacketing (FRP). Among the various retrofitting methods of reinforced concrete columns, steel jacketing is one of the methods used to strengthening of RC structures, especially for confining RC columns with rectangular and square cross sections. Steel cage is a type of steel jacket and because of its effectiveness, ease of use, light weight and the availability of material, it has become an affordable, effective, economic and simple option. This method involves the use of four longitudinal angle steel profiles fixed to the corners of the RC columns, to which some transverse steel strips are welded. The gap between steel cage and column is filled with cement or epoxy mortar. Different parameters affect the behavior of the column reinforced with steel cage. Studies carried out on this strengthening method have mostly focused on the axially loaded columns. The parameters have been studied are the number of steel strips, the size of the steel strips, the size of the steel angels, the thickness of the steel strips, the yield stress of the steel of the cage, the compressive strength of the concrete used in the column, and, finally, the use of capitals in the beam-column connection joint zone. Capitals are welded to the steel cage and located at each end of the cage, loads applied to the beam are transmitted to the steel cage through the capitals. Loads from an upper floor of the building are also transmitted to the cage through the beam via the capitals. Current study investigates the behavior of RC columns strengthened with steel cage under axial force and bending moment. In this regard, the strengthened RC column with steel cage was modeled using finite element method using ABAQUS software and calibrated by experimental results obtained from other laboratory research works. Then, the parameters affecting the behavior of the strengthened columns were examined. The results of this study show a good agreement with experimental results and demonstrate a considerable increase in the ultimate axial force and bending moment.

Service life and safety of a steel jacket platform is influenced by vibrations generated by environmental loads, waves and winds. Vibrations of the structure and deck may cause fatigue in the structural elements and joints. Also may disrupt the operation of the drilling equipment and facilities as well as the operation of the platform. Therefore, the main aim of this research is to control the vibrations of the steel jacket platform through shape memory alloys dampers. Shape memory alloys have two important properties of shape memory as well as superelastic behavior and are quite suitable for damping applications. In these alloys, crystal structures transition from the austenite to the martensite phase, and vice versa are accompanied by the energy dissipation. In this research, a 90m steel jacket structure equipped with SMA dampers installed in 80m water depth has been modeled as a multi-degree-of-freedom system and analyzed under the time history of wave loads. For solving the differential equations of system vibration and modeling the hysteresis behavior of the shape memory alloys elements, the direct integration alpha method and multi-linear idealized constitutive model have been used, respectively. Jacket platform equipped with the shape memory alloys dampers shows the better result with 42% reduction in deck displacement, 62% reduction in deck acceleration and 32% reduction in shear force of platform base.

Most of the destructive effects of blast loading on structures can be found in the form of local failure of structural members. Such local damages could be associated with progressive collapse of the whole building. Progressive collapse, which has caused widespread casualties and financial losses at the blast events, can occur as a result of the sudden collapse and removal of structural columns under direct effect of the blast pressure. Therefore, assessment of the blast response of RC columns and their retrofitting against blast loading would provide very useful information in the field of blast resistant structures. In this paper, using a validated FE modeling process, square RC columns and RC columns strengthened with steel jacketing under blast loading, are analyzed by the explicit solver of ABAQUS software package. By performing nonlinear dynamical analyses, the explosive response of simple and strengthened RC column models are compared in terms of maximum displacement values ​​and absorbed energy. Obtained results show that retrofitting of RC columns with steel jackets, significantly reduces the energy reaching the structure and the deformation, and improves the performance against blast loading.

Reinforced concrete (RC) structures are widely used in urban buildings and infrastructures, and these are always subjected to explosions caused by intentional or unintentional accidents. Among the structural members, columns are key load carrier elements. In this paper, behavior of RC columns with circular and square sections strengthened by steel jackets is investigated and compared under blast loading. Accordingly, six circular columns and six square columns, which are equivalent in geometry and material properties, were modeled using ABAQUS software package. The effect of varying the concrete strength, longitudinal reinforcement and geometrical properties of steel jacket on FE models of the columns has been studied. In addition, a sub-program has been written to evaluate the changes in axial and lateral capacity of the column. Based on the most important results, the circular columns perform better under blast loading. Using steel jackets, in addition to increasing the explosive capacity of the column, improves the effects of other remediation strategies such as the use of high strength concrete and the higher percentage of reinforcement. This effect was observed to be higher in circular columns in compare to square columns.

In the current study, the effect of the extreme lateral loading on the square and circular Reinforced Concrete (RC) columns with and without retrofitting was investigated. 3D finite element modeling of the columns and impact loading condition was performed using the ABAQUS/Explicit software. The data of a real scale blast test carried out in our previous study were used to verify the modeling accuracy. The effect of secondary moments due to axial load, different geometrical characteristics of the steel jacket, compressive strength of the concrete, and the longitudinal reinforcement on the explosive capacity of the column and its residual axial strength were studied. Results showed that the circular columns perform better under the sudden lateral pressure than equivalent square ones. Also, steel jacketing increased the explosive capacity of the column, which was more effective in the circular columns than the square ones. The results also indicated that steel jacketing with less buckling capacity had the least improvements on the column capacity. It was found that the effects of the initial axial force in the column were significant on its behavior under explosive loading condition, which should be taken into account in any modeling approaches. In general, the P-δ phenomenon had less effect on the circular columns than the square ones. Also, the use of a high-strength concrete and a higher percentage of longitudinal reinforcement further influenced the retrofitted columns than unretrofited (normal) ones, which was more evident in the circular columns in comparison with square columns.